In use in popular ignition systems for internal combustion engines is an ignition coil or coils having an iron core, i.e. ferro-magnetic, within a non-conductive housing, with the primary and secondary windings wound on individual bobbins inter-nested within one another and lying within the boundaries of the iron core, and with a portion of the core, i.e. an elongated leg, extending through the inner most bobbin along its axis. The coil is filled with epoxy potting material or other insulating material as a final step in the process. It is known that the efficiency can be increased and compactness of the overall coil structure, including the housing, can be reduced by providing a permanent magnet between the core portion surrounded by the coil windings and the remainder of the core, as well as also providing an air gap between the permanent magnet and the outer part iron core, i.e. that part of the core forming the outer closed magnetic circuit.
Such a coil construction is shown in U.S. Pat. No. 4,990,881. Part of the success in making such a coil design commercially practical has been the discovery of a very strong permanent magnetic material containing such elements as samarium (Sm), neodymium (Nd), and other similar rare earth, high energy materials. The permanent magnet used is made entirely of such material and referred to as "fully dense". The air gap of the iron core of the ignition coil, although reduced by insertion of the magnet, is still retained in the design of the aforementioned coil.
In contrast, in the subject invention a permanent magnet-type ignition coil is provided having preferably no air gap and also assuring that should there be a small air gap due to component tolerance stack-up it will be in a predetermined location thereby enhancing considerably the efficiency and power output of the coil. This allows for a substantial reduction in the size of the overall unit for acquiring the same unit power output. A further feature of the subject invention is the design and use of a permanent magnet composed of a bonded magnetic material, which is less than fully dense, made of these most recently available rare earth, high energy materials such as samarium and neodymium, thereby providing a material which is equally effective, but far less expensive than the fully dense permanent magnet heretofore used, and having the added benefit that its thickness, including the magnetizing alloy elements Nd or Sm or equivalent, provides for less expensive fabrication and easier handling during assembly of the coil.
Also in use are in ignition systems employing a wasted spark configuration, which have twin coil towers at opposite ends of the same coil assembly. A single ignition tower is provided for each spark plug in the engine. Thus a two cylinder engine has a single coil assembly, and a four cylinder engine has two coil assemblies, etc. For such systems, the coil assembly may be entirely different structures, i.e. the housings and connectors may be entirely different for one operation as opposed to another. Thus, each may require unique tooling or manufacturing techniques, thereby greatly increasing tooling and manufacturing complexity and costs. Another alternative is modular design and construction, accomplished by having pairs of coil connected to a coil, inserted within a housing having connectors on the housing that allow multiple housings to be connected in series. However, having this chain of coil housings connected together is not an efficient use of space.